Bentley to debut world's fastest four-seat convertible at NAIAS 2013

On January 14, the Bentley Continental GT Speed Convertible makes its international debut at the North American International Auto Show in Detroit. Boasting a six-liter twin-turbocharged 48-valve W12 engine, improved suspension, all-wheel drive and a top speed of 202 mph (325 km/h), Bentley claims it is the world’s fastest four-seat convertible.

Getting performance out of a convertible is always tricky. Cars rely on the roof for structural integrity and chopping it off means adding a lot of reinforcement to make up for the loss. The Continental GT Speed Convertible weighs in at 2,900 kilograms (6,393 lb) as opposed to the Speed coupé’s 2,750 kilograms (6,063 lb), yet despite the extra weight it manages to lag behind the coupé by only 5 km/h (3 mph).

From the outside, the Continental GT Speed Convertible is definitely a Bentley with its subdued lines and the boxy profile of its exceptionally rigid body shell. It tries to be a bit more sporty than its fellow Bentleys with its 21-inch alloy wheels, dark-tint matrix grilles, “rifled” elliptical exhaust tailpipes, and front wings in superformed aluminum, but you get the feeling that it’s fighting with itself about what sort of car it wants to be. Is it “creating an impression of tension and muscularity” as Bentley claims, or is it still the car your bank manager drives?

Inside, the Speed Convertible has the same powertrain as the GT Speed coupé. The six-liter twin-turbocharged 48-valve W12 punches out 616 bhp (460 kW, 625 PS) and 800 Nm (590 lb/ft) of torque – all held in check by the ME17 engine management system. This crunches 180 million calculations per second as it enhances the turbocharger control and torque management. As with other W12-engined models, there is an energy recuperation system. Fuel consumption is 14.9 liters/100km (19.0 mpg) – 15 percent better than the Speed coupé.

Backing up the engine is a flappy-paddle ZF eight-speed automatic gearbox with Quickshift, Block Shifting and permanent all-wheel drive with a 40:60 rear bias that Bentley claims provides optimum traction and power in all road conditions. According to Bentley, the upshot of all this is sharper throttle response, gear-shifting at higher engine speeds and faster “block shifting.”

Bentley has re-tuned the rack and pinion, power assisted, speed-sensitive ZF servotronic steering for the Speed Convertible and uprated and lowered the suspension. The front suspension consists of four link aluminum double-wishbones, computer controlled self-leveling air suspension with anti-roll bar, while the rear boasts trapezoidal multi-link, computer-controlled self-leveling air suspension. These have Continuous Damping Control tuned for dynamic performance. Standard brakes are 405 mm ventilated discs in front and in the back are 335 mm ventilated discs. Cross-drilled Carbon silicon carbide versions are available as an option.

The Speed Convertible’s top speed of 325 km/h (202 mph) is matched by a respectable bit of acceleration that sees it going from 0-96.5 km/h (60 mph) in 4.1 seconds, 0-100 km/h (62 mph) in 4.4 seconds and 0-160 km/h (100 mph) in 9.7 seconds. Despite this burst of speed, Bentley says that spoilers are unnecessary because the lip on the bootlid generates enough downforce to keep the Speed Convertible on the tarmac even when going flat out.

One interesting touch that Bentley is keen to point out is that “the enhanced performance is accentuated by a glorious baritone snarl from the free-breathing exhaust.” It’s not exactly what you expect from a Bentley. No doubt it’s very cool, but given Bentley’s stately reputation, it’s also a bit like finding out your aunt Agatha has taken up free-base jumping.

Things quiet down a bit in the Speed Convertible’s interior with diamond-quilted hide upholstery and a finish inspired by the Le Mans-winning Bentleys of the 1920s. On a more modern note, there’s an infotainment system with 15 GB of available storage space which can be expanded via an SD card, connectivity for an iPod or MP3 player, and a built-in six-disc CD changer. For those worried about the weather, Bentley says that the hood can take on a monsoon (presumably when up) and when it’s down, there’s a neck warmer to keep the chill off.

No price has been set, but with the coupé enjoying a starting price of US$217,725, this one is not in the econocar bracket.

UPDATE: We've added more pics from the show floor in Detroit to the gallery.